The Collaborative International Dictionary of English v.0.48:

Practicability \Prac"ti*ca*bil"i*ty\, n.
   The quality or state of being practicable; practicableness;
   feasibility. "The practicability of such a project."
   --Stewart.
   [1913 Webster]

WordNet (r) 3.0 (2006):

practicability
    n 1: the quality of being usable [syn: practicability,
         practicableness] [ant: impracticability,
         impracticableness]